This invention relates to medical electrical leads in general, and to endocardial screw-in pacing leads, in particular.
In an effort to assure the stable location of an endocardial pacing electrode, a variety of approaches have been employed. One common approach is to employ an endocardial pacing lead which has a sharpened helix located at its distal end. This helix may either be the pacing electrode, or may be located adjacent the pacing electrode. The helix is rotated by some means from the proximal end of the lead and screwed into the endocardium, to permanently locate the electrode within the heart.
Within the general field of endocardial screw-in pacing leads, a number of different varieties have emerged. Early designs employed helixes that were fixedly mounted with respect to the end of the pacing lead, such as that disclosed in German Patent No. 2533766, 2539553, issued to Osypka. In this lead, rotation of the helix into the heart tissue was accomplished either by rotation of the entire lead, or by rotation of a stylet with a screwdriver tip, which engaged a slot located internal to the pacing lead, adjacent its distal end.
Later designs employed fixation helixes that were advanceable from or retractable into the distal end of the pacing lead to facilitate passage of the pacing lead through the venous system and through the tricuspid valve, one such lead is illustrated in U.S. Pat. No. 4,106,512 issued to Bisping. This patent discloses a lead in which the helix acts as the electrode, and is advanced out of the distal end of the lead by rotation of the coiled conductor within the lead body. An alternative approach to Bisping is illustrated in U.S. Pat. No. 4,217,913, issued to Dutcher. In this patent, a screwdriver tip stylet is employed to rotate the fixation helix out of the distal end of the lead. In this embodiment, the helix serves only to attach the lead to the tissue, and a separate ring electrode is supplied for stimulation purposes. In this lead, the stylet engages a slot within the distal end of the lead, located on a member which rotates with the fixation helix.
Yet another approach is illustrated in U.S. Pat. No. 4,570,642 issued to Kane et al. In this embodiment, the helix is located on a member which is slidable within the distal end of the pacing lead, and is advanced out of the distal end of the pacing lead by means of a cylindrical stylet which pushes a member located within the distal end of the lead, carrying the fixation helix. The fixation helix is screwed into the tissue by rotation of the entire lead.
Both the Kane and Dutcher leads disclose fixtures mountable on the connector pin of the pacing lead for facilitating employment of the helix. In the Dutcher lead, the fixture serves as a ratchet, allowing for advancement of the fixation helix out of the distal end of the lead. In Kane, the fixture stabilizes the longitudinal relationship of the stylet and pacing lead in order to hold the helix in an extended position.